broadcom/compiler: allow color TLB writes in last instruction

Only Z writes are disallowed.

total instructions in shared programs: 11578449 -> 11577369 (<.01%)
instructions in affected programs: 38132 -> 37052 (-2.83%)
helped: 1080
HURT: 0
Instructions are helped.

total max-temps in shared programs: 2334416 -> 2334395 (<.01%)
max-temps in affected programs: 218 -> 197 (-9.63%)
helped: 21
HURT: 0
Max-temps are helped.

total inst-and-stalls in shared programs: 11607890 -> 11606810 (<.01%)
inst-and-stalls in affected programs: 38265 -> 37185 (-2.82%)
helped: 1080
HURT: 0
Inst-and-stalls are helped.

total nops in shared programs: 338316 -> 337236 (-0.32%)
nops in affected programs: 2625 -> 1545 (-41.14%)
helped: 1080
HURT: 0
Nops are helped.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13964>

src/broadcom/compiler/nir_to_vir.c

@@ -1757,6 +1757,7 @@ emit_frag_end(struct v3d_compile *c)
                 inst->uniform = vir_get_uniform_index(c, QUNIFORM_CONSTANT,
                                                       tlb_specifier |
                                                       0xffffff00);
+                inst->is_tlb_z_write = true;
         }
 
         /* XXX: Performance improvement: Merge Z write and color writes TLB

src/broadcom/compiler/qpu_schedule.c

@@ -1503,10 +1503,7 @@ qpu_inst_valid_in_thrend_slot(struct v3d_compile *c,
 {
         const struct v3d_qpu_instr *inst = &qinst->qpu;
 
-        /* Only TLB Z writes are prohibited in the last slot, but we don't
+        if (slot == 2 && qinst->is_tlb_z_write)
-         * have those flagged so prohibit all TLB ops for now.
-         */
-        if (slot == 2 && qpu_inst_is_tlb(inst))
                 return false;
 
         if (slot > 0 && qinst->uniform != ~0)

src/broadcom/compiler/v3d_compiler.h

@@ -169,6 +169,9 @@ struct qinst {
          * otherwise.
          */
         int uniform;
+
+        /* If this is a a TLB Z write */
+        bool is_tlb_z_write;
 };
 
 enum quniform_contents {